1. Field of the Invention
The present invention relates generally to the field of fuel cells and, more specifically, to a thermal management system that integrates a direct methanol fuel cell (DMFC) system and a device, in which the device is powered at least in part by the DMFC.
2. Background Information
Fuel cells are devices in which an electrochemical reaction is used to generate electricity. A variety of materials may be suited for use as a fuel depending upon the materials chosen for the components of the cell. Organic materials, such as methanol or natural gas, are attractive choices for fuel due to their high specific energy.
Direct oxidation fuel cell systems may be better suited for a number of applications in smaller mobile devices (e.g., mobile phones, handheld and laptop computers), as well as in some larger applications. Typically, in direct oxidation fuel cells, a carbonaceous liquid fuel in an aqueous solution (typically aqueous methanol) is introduced to the anode face of a membrane electrode assembly (MEA). The MEA contains a protonically-conductive, but electronically non-conductive membrane (PCM). Typically, a catalyst which enables direct oxidation of the fuel on the anode is disposed on the surface of the PCM (or is otherwise present in the anode chamber of the fuel cell). Diffusion layers are typically in contact with at least one of the catalyzed anode and cathode faces of the PCM to facilitate the introduction of reactants and removal of products of the reaction from the PCM, and also serve to conduct electrons. Protons (from hydrogen found in the fuel and water molecules involved in the anodic reaction) are separated from the electrons. The protons migrate through the PCM, which is impermeable to the electrons. The electrons thus seek a different path to reunite with the protons and oxygen molecules involved in the cathodic reaction and travel through a load, providing electrical power.
One example of a direct oxidation fuel cell system is a direct methanol fuel cell system or DMFC system. In a DMFC system, methanol in an aqueous solution is used as fuel (the “fuel mixture”), and oxygen, preferably from ambient air, is used as the oxidizing agent. There are two fundamental half reactions that occur in a DMFC which allow a DMFC system to provide electricity to power consuming devices: the anodic disassociation of the methanol and water fuel mixture into CO2, protons, and electrons; and the cathodic combination of protons, electrons and oxygen into water. The overall reaction may be limited by the failure of either of these reactions to proceed to completion at an acceptable rate (more specifically, failure to oxidize the fuel mixture will limit the cathodic generation of water, and vice versa).
Typical DMFC systems include a fuel source, fluid and effluent management systems, and a direct methanol fuel cell (“fuel cell”). The fuel cell typically consists of a housing, and a membrane electrode assembly (“MEA”) disposed within the housing. A typical MEA includes a centrally disposed protonically conductive, electronically non-conductive membrane (“PCM”) such as Nafion®, a registered trademark of E. I. Dupont de Nours and Company, which is a cation exchange membrane comprised of perfluorosulfonic acid, in a variety of thicknesses and equivalent weights. The PCM is typically coated on each face with an electrocatalyst such as platinum, or platinum/ruthenium mixtures or alloy particles. On either face of the catalyst coated PCM, the MEA typically includes a diffusion layer. The diffusion layers function to evenly distribute the liquid and gaseous reactants to, and transport the liquid and gaseous products of the reactions from the catalyzed anode face of the PCM, or the gaseous oxygen from air or other source across the catalyzed cathode face of the PCM. The diffusion layers also facilitate the collection of electrons and conduction to the device being powered. In addition, flow field plates may be placed on the aspect of each diffusion layer that is not in contact with the catalyst-coated PCM to provide mass transport of the reactants and by products of the electrochemical reactions and also have a current collection functionality to collect and conduct electrons through the load.
One problem with electronic systems and components, including those which may be powered by DMFC systems, is that electronic components and subsystems can become overheated, and their performance compromised. This problem is especially difficult to effectively address in small mobile devices where electronic components are packed tightly together and space, weight, and volume are critical design criteria. In such devices, it is desirable to minimize the number of components dedicated to cooling the system. Also, as mobile devices become more powerful and require more power, mobile device components produce increasing amounts of heat. Accordingly, it is increasingly important to remove heat from the electronic components and systems.
DMFCs are efficient at dissipating heat that is generated within the system, due to the fact that there are several fluids present in the system, and due to the fact that air is exchanged within the fuel cell system, allowing for a more natural heat exchange. In addition, the direct oxidation fuel cell systems and DMFCs demonstrate increased current generation (at a given voltage) at higher temperatures due to the increased kinetics of the reactions. Thus, if additional heat is applied to the reaction, the DMFCs can become an even more suitable power source.
It is thus an object of the invention to provide a thermal management system that provides temperature regulation of a device powered at least in part by a DMFC system, in which excess heat produced by the device is transferred to the DMFC. As a result of this heat transfer, the temperature of the device is kept within a desired range and the operation of the DMFC is improved.